Enabling the Read-Only Mode for ClickHouse Tables

This topic is available for MRS 3.2.0 or later only.

Scenario

During data migration, one-click balancing, decommissioning and capacity reduction, ClickHouse allows you to set the only_allow_select_statement parameter for MergeTree series tables to enable SELECT operations instead of ALTER, RENAME, DROP, and INSERT operations.

Procedure for Enabling the Read-Only Mode of the ClickHouse Table

Install the client. For details, see Installing a Client.
Run the following commands to log in to the node where the client is installed as user root:

cd Client installation directory

source bigdata_env
Run the following command to authenticate the user if the cluster is in security mode (with Kerberos authentication enabled). Otherwise, skip this step.

kinit Component service user

The user must have the ClickHouse administrator permissions.
Run the proper client command to connect to the ClickHouse server.
- Normal mode
  clickhouse client --host IP address of the ClickHouse instance--user Username --password --port 9440 --secure
  
  Enter the user password.
- Security mode
  clickhouse client --host IP address of the ClickHouse instance--port 9440 --secure
- For a cluster in normal mode, the username is default. Alternatively, you can create an administrator using the open source ClickHouse web UI. Do not use the users created on FusionInsight Manager.
- To obtain the IP address of the ClickHouseServer instance, log in to FusionInsight Manager, choose Cluster > Services > ClickHouse, and click the Instance tab.
Run the following statement to set the table to read-only:

ALTER TABLE {table_name} MODIFY SETTING only_allow_select_statement = true;

Disabling the Read-Only Mode of the Table

Log in to the ClickHouse client by referring to 2 to 4.
Run the following statement to disable the read-only mode of the table:

ALTER TABLE {table_name} MODIFY SETTING only_allow_select_statement = false settings hw_internal_operation = true;